Among compounds having a basic skeleton of pyridonecarboxylic acid there have been known a variety of compounds useful as synthetic antibacterial agents, since they have excellent antibacterial activity and a wide antibacterial spectrum. Of these, in the clinical field, as therapeutic agents for infectious diseases there have been widely used compounds such as norfloxacin (Japanese Patent Application Laid-Open (kokai) No. 53-141286), enoxacin (Japanese Patent Application Laid-Open (kokai) No. 55-31042), ofloxacin (Japanese Patent Application Laid-Open (kokai) No. 57-46986), ciprofloxacin (Japanese Patent Application Laid-Open (kokai) No. 58-76667), and tosufluoxacin (Japanese Patent Application Laid-Open (kokai) No. 60-228479).
However, these compounds are not perfectly satisfactory in terms of antibacterial activity, intestinal absorption efficiency, stability in metabolism, and side effects, inter alia, phototoxicity and cytotoxicity.
In view of the foregoing, an object of the present invention is to provide pyridonecarboxylic acid-based antibacterial agents which have satisfactory antibacterial activity, intestinal absorption efficiency, stability in metabolism, and acceptable side effects particularly in terms of phototoxicity and cytotoxicity; and to provide intermediates for synthesis thereof.